Apc-mutants act as supercompetitors in intestinal tumour initiation

Almost all colorectal cancers (CRC) present with mutations in the Apc gene, leading to unrestrained Wnt activation and the initiation of tumour development. We previously reported the competitive benefit of Apc-mutant intestinal stem cells (ISCs) within the crypt, however, the mechanism by which they outcompete their wild type (WT) neighbours remained elusive. Here, we studied the effect of Apc-mutants using an in vitro culture system of WT (Lgr5-CreErt2) and Apc-/- (Lgr5-CreErt2;Apcfl/fl) organoids . The expression patterns of WT and Apc-/- organoids revealed significant upregulation in specific secreted Wnt antagonists Notum, Wif1 and Dkk2. Furthermore, we studied the effect of the secreted antagonist by treating WT organoids with either WT or Apc-/- conditioned medium (CM) for 48 hours and observed a significant decrease in stem cell markers and an increase in goblet cell markers. We report that Apc-mutants act as bona fide supercompetitors by secreting Wnt antagonists that result in active differentiation of WT ISCs. Overall design: Intestinal organoids of Apc-mutant (Day2 n=3, Day 4 n=3); wild-type (Day 2 n=3, Day 4 n=3); Apc-mutant treated with Apc-mutant conditioned medium (Day 2 n=3); wild-type treated with Apc-mutant conditioned medium (Day 2 n=3)